Valve spring processing

ABSTRACT

COILED STEEL INTERNAL COMBUSTION ENGINE VALVE SPRINGS ARE PRODUCED BY HARDENING CARBON STEEL WIRE, TEMPERING THE HARDENED WIRE TO AN RC HARDNESS OF 50 TO 51 AT ABOUT 700*F., COILING THE TEMPERED WIRE INTO SPRINGS, AND THEN STRESS RELIEVING THE COILED SPRINGS AT A TEMPERATURE ABOVE THE TEMPERING TEMPERATURE AND TO A HARNESS NOT SIGNIFICANTLY GREATER THAN RC 47. THIS RESULTS IN A SPRING STEEL OF DEFINITELY HIGHER RESISTANCE TO RELAXATION IN SERVICE.

J1me 1971 w. M. JusTussoN VALVE SPRING PROCESSING 3 Sheets-Sheet 1 FiledApril 21, 1969 mfimmz mwm 9 6 7 w 4 4 4 4 m w W W 0. w E R w M m H. m EM M M M Q m D E T M w w mi m M W r w 0 N w w M W S C S 4 w m M M w 0 0 Mw 0 0 0 0 0 0 0 0 0 0 STRESS RELIEF TEMR OF I NVENTOR W/ZZl/IM M.JUSTOJLSO/V BY MI, /9 744,44. 7% I 042161,

ATTORNEYS June 29, 1971 w. M. JUSTUSSON 3,589,950

VALVE SPRING PROCESSING Filed April 21. 1969 s Sheets-Sheet 2 HARD w RESPR N65 U 49 t v w 46 m g 47 c PQODUCTION w/m? SPRINGS E 45 WV 7 W RELAXAT/O/ TEST STRESS REL IE w/va TEMI? F INVENTOR W/ZZ/A/V/ M JUSTUJJO/VZQQMJo VCCLuXQ ATTORNEYS United States Patent 3,589,950 VALVE SPRINGPROCESSING William M. Justusson, Farmington, Mich., assignor to FordMotor Company, Dearborn, Mich. Filed Apr. 21, 1969, Ser. No. 817,982Int. Cl. 021d 1/18, 9/02 US. Cl. 14812 2 Claims ABSTRACT OF THEDISCLOSURE Coiled steel internal combustion engine valve springs areproduced by hardening carbon steel Wire, tempering the hardened wire toan R0 hardness of 50 to 51 at about 700 F., coiling the tempered wireinto springs, and then stress relieving the coiled springs at atemperature above the tempering temperature and to a hardness notsignificantly greater than Re 47. This results in a spring steel ofdefinitely higher resistance to relaxation in service.

BACKGROUND OF THE INVENTION The wire coil springs employed to seat thevalves in internal combustion engines undergo very severe conditions inservice and are a very critical item in the operation of the engine.These springs are ordinarily produced from carefully processed SAE 1070steel. These springs have a tendency to relax or deteriorate inload-carrying ability with time and usage at the moderate temperaturesto which they are exposed in normal engine operation. This relaxationcan lead particularly at high speed to valve throwing. Either of theseconditions can yield to a failure of the valves to seat properly withcatastrophic efl ect upon the operation of the engine.

Currently, internal combustion engine valve coil springs are fabricatedfrom carefully selected SAE 1070 wire which has been hardened, usuallyby an oil quench. This hardened wire is then tempered at about 800 F.for 30 minutes or to a hardness of R0 43 to 47. This tempered wire iscoiled at ambient temperatures and then stress relieved at 750 F. forthirty minutes. It is to be noted that this stress relieving temperatureis lower than the tempering temperature and has essentially no eifectupon the hardness of the coiled springs.

Relaxation of these springs is determined by initially compressing thespring to a preselected dimension, measuring the spring load at thispreselected dimension, exeouting the test, and then again compressingthe spring to the same preselected dimension and measuring the load. L

The difierence between the first and second load is the springrelaxation and is expressed in terms of the percentage of the originalload.

Production test springs are required to survive 10' cycles at ambienttemperature at a maximum shear stress of 115,000 pounds per square inchwith no more than five percent relaxation.

THE INVENTION This invention involves the hardening of SAE 1070 steeland then tempering it at a temperature of about ice 700 F. which willresult in a hardness of Re 50 to 51. The diameter of the wire is 0.186inch. This wire was formed into coils by winding it around a mandrel0.981 inch in diameter to give a spring as formed having a diameter of1.016 inches.

The coiled springs so produced were then given stress relieving thermaltreatments at temperatures including temperatures above the originaltempering temperature.

FIG. 1 is a graph depicting the stress relieving tem perature forone-half hour plotted against the spring hardness and spring diameter.It will be noted that the diameter of the spring decreases from 1.016 to1.003 inches and the hardness from Rc 51 to R0 47 as the stressrelieving temperature rises to 775 F. This temperature produces ahardness of Rc 47 which is the upper limit not employed.

FIG. 2 again emphasizes the stress relieving temperature and graphs thisvalue against hardness and relaxation. The upper portion of FIG. 2clearly shows that the stress relieving treatment has no effect upon thehardness of ordinarily produced coiled springs. The decidedly superiorqualities of the product of this invention (hard wire) over conventionalsprings, insofar as relaxation at elevated temperature, is shown by thisdrawing.

FIG. 3 is a showing of the properties of conventional springs and thehard wire springs of this invention when subjected to static shear testsat various shear levels and at 275 F. for 48 hours.

This very specific process for the production of superior coil valvesprings for internal combustion engines enables the use of low costcarbon steel and a decided reduction in the weight of the springs withno sacrifice in performance or durability.

I claim as my invention:

1. The process of producing a relaxation resistant internal combustionengine valve coil spring comprising hardening spring wire formed fromsteel metallurgically equivalent to SAE 1070 steel, tempering thishardened wire at about 700 F. or to a hardness of Re 50 to 51, coilingthis tempered wire about a mandrel to produce a coil spring larger indiameter than the final spring, and stress relieving the coiled springat a temperature higher than the tempering temperature to cause thespring to contract in diameter and exhibit a hardness not substantiallyabove Rc 47.

2. The process recited in claim 1 in which the stress relievingtemperature is approximately 775 F.

References Cited FOREIGN PATENTS 9/1960 Great Britain 29173 CHARLES N.LOVELL, Primary Examiner US. Cl. X.R.

